Researchers attempting to establish neural correlates of behavior commonly study invertebrate model preparations such as Aplysia for practical reasons. This line of research will be extended by studying a complex behavior, migratory swimming. Migrations of opisthobranchs, including Aplysia, have been both claimed and refuted in the literature but the critical data on movement of identified individuals are lacking. Swimming in Aplysia has been documented, but the orientational mechanisms involved and the factors responsible for the initiation of swimming have not been determined. Preliminary observations showed that large Aplysia swam on the surface in an inlet between islands on the incoming tide during late March, and were transported to the protected grassbeds of the Intracoastal Waterway. Copulating adults and very small Aplysia were encountered in these grassbeds during April and May. By late June, small to medium size Aplysia were again encountered swimming in inlets, but on the outgoing tide. Experimental releases of adult Aplysia in shallow nearshore water showed that individuals tended to swim in similar directions when released repeatedly, and to swim in the offshore direction at the release site. At higher current velocities, Aplysia modified their swimming effort depending on their direction of swimming relative to current direction, thus achieving a more constant ground speed. We propose to expand upon these preliminary observations in several ways during an 8 week field study during the spring migratory period. Observations on the number of animals swimming in inlets every 6 days will reveal any peak(s) in this activity. Daytime observations on the frequency of swimming in inlets at different tidal phases will reveal if Aplysia use tidal currents to facilitate displacement, as has been reported for other species. Tracking of Aplysia having sonic transmitters attached will reveal details of behavior during the migratory periods as well as the magnitude of displacement and duration of swimming of individuals. Finally, sets of experimental releases will be conducted in the presence of different combinations of directional stimuli to determine what directional cues and sensory modalities are involved in the orientation of swimming.